The computer aids in selecting compounds for antitumor screening. An estimate of the probability of activity of a new compound is derived from its structural features based on chemical and biological data from testing about 50,000 compounds in the mouse lymphocytic leukemia (P388) screen. Also, the incidence of its least occurring structural feature in P388 testing is considered a measure of novelty of the new compound. These measures, as well as comparison with a series of about 100 desired profiles, are used in two modes. One, all potential acquisitions are rated and this information is used along with the structures in deciding which compounds to acquire or which to exclude. Two, as an experiment in literature surveillance, CAS registrations are being run through a specially designed version, capable of handling all reported chemical structures at low cost. As this work moves into production, research is pointed toward evaluation, improvement and further scope of application.